<?php
//class elo_calculator
//{
function rating($S1, $S2, $R1, $R2)
    {
        if (empty($S1) OR empty($S2) OR empty($R1) OR empty($R2)) return null;
        if ($S1 != $S2) {
            if ($S1 > $S2) {
                $E = 120 - round(1 / (1 + pow(10, (($R2 - $R1) / 400))) * 120);
                $R['R3'] = $R1 + $E;
                $R['R4'] = $R2 - $E;
            } else {
                $E = 120 - round(1 / (1 + pow(10, (($R1 - $R2) / 400))) * 120);
                $R['R3'] = $R1 - $E;
                $R['R4'] = $R2 + $E;
            }
        } else {
            if ($R1 == $R2) {
                $R['R3'] = $R1;
                $R['R4'] = $R2;
            } else {
                if ($R1 > $R2) {
                    $E = (120 - round(1 / (1 + pow(10, (($R1 - $R2) / 400))) * 120)) - (120 - round(1 / (1 + pow(10, (($R2 - $R1) / 400))) * 120));
                    $R['R3'] = $R1 - $E;
                    $R['R4'] = $R2 + $E;
                } else {
                    $E = (120 - round(1 / (1 + pow(10, (($R2 - $R1) / 400))) * 120)) - (120 - round(1 / (1 + pow(10, (($R1 - $R2) / 400))) * 120));
                    $R['R3'] = $R1 + $E;
                    $R['R4'] = $R2 - $E;
                }
            }
        }
        $R['S1'] = $S1;
        $R['S2'] = $S2;
        $R['R1'] = $R1;
        $R['R2'] = $R2;
        $R['P1'] = ((($R['R3'] - $R['R1']) > 0) ? "+" . ($R['R3'] - $R['R1']) : ($R['R3'] - $R['R1']));
        $R['P2'] = ((($R['R4'] - $R['R2']) > 0) ? "+" . ($R['R4'] - $R['R2']) : ($R['R4'] - $R['R2']));
        return $R;
    }
//}
?>